The present disclosure relates to thermally actuated flow-control valves. More particularly, the present disclosure relates to valves including wax-filled actuators employed to control the flow of transmission fluid or coolant in automatic transmissions or other heat producing automotive systems.
The use of wax-filled actuators or wax motors in automotive systems is well known. Wax actuators typically utilized in automotive systems are employed to regulate the flow of engine fluids and prevent overheating. Such actuators are designed to open or close in response to a predetermined change in temperature. Wax-filled actuators are reliable temperature sensitive actuators that require no external energy, such as electricity or externally applied actuation force, such as a cable or lever.
In temperature sensitive automotive systems, there is no or restricted flow of fluid to designated fluid passages when the fluid is cool and the wax actuator is closed. As the fluid warms up, the wax actuator begins to open, and permits fluid to flow. As the temperature of the fluid increases, the wax actuator progressively reaches its fully open, or fully “stroked” position, when the fluid reaches a predetermined operating temperature. The wax actuator fluctuates between the nominal opening position and the fully stroked position as the temperature of the engine fluctuates.
The wax actuator conventionally comprises a rigid wax-filled cup, a guide and a piston received within the guide. The wax transitions between a solid and a liquid state over a predetermined temperature range, and typically expands in volume as the wax becomes a liquid. The guide is fixed to the cup and retains a flexible diaphragm to contain the wax in the cup. The guide defines an axial passage for a piston, which reciprocates in the axial passage according to pressure from the wax beneath the diaphragm. Thus, the axial length of the actuator changes according to the temperature of the wax, which is responsive to the temperature of the surrounding fluid.
The wax-filled actuator is typically contained in a housing or aperture, with the piston arranged to deliver the force of the expanding wax to move the actuator body (the cup/guide) which may include a disc valve affixed to the piston, the cup/guide, or both. A return spring is also positioned to return the piston to its retracted/cold position when the temperature of the fluid falls and the wax returns to its smaller volume. The return spring is selected to overcome the friction of the piston in the axial passage and any linkage or valve associated with the actuator, to ensure reliable return to the closed or cold position.
In prior art wax-filled actuators of this type, there is a trade-off between the space occupied by the device, and the amount of fluid flow through the system. Under certain circumstances, the size and structure of the actuator may inhibit the effective flow of fluid through the system. Decreased fluid flow is particularly troublesome in systems having sensitive components requiring an adequate supply of fluid, yet other structural considerations limit the free space that the actuator may travel between the open and closed positions. Thus, spacial constraints limit the effectiveness of wax actuators in certain environments.
Consequently there exists a need for a simple thermally actuated flow-control valve that allows fluid to flow efficiently through the system with a limited amount of travel between the open and closed positions.